Hi!
FWIW the U.S. National Transportation Safety Board considers 0.2 degrees the minimum angle for detecting an aircraft coming straight at you. See
this article from
Aviation Week and Space Technology. This corresponds to a distance of about 20 feet at a range of one mile under good seeing conditions, so you could see an on-coming B-24 (wingspan: 110 feet) at a range of about 5.5 miles (8-9 km) in perfect weather.
That being said, the U.S. Army air defense folks list a whole bunch of reasons (
in this document) why real life detection ranges can be much shorter, including:
- Aircraft size
- Viewing aspect
- Contrast with background
- Visibility
- Terrain masking (not much over the ocean)
- Camouflage
- Visual acuity of the observer
- Search sector for watch crewmen (smaller sector = better detection chance)
IMHO the odds of hearing an aircraft over the sound of your own diesel engine exhaust (remember, the exhaust port is underneath the AA gun platform) are pretty small.
Short answer: "it depends"
Pablo
__________________
"...far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows neither victory nor defeat."
- Theodore Roosevelt,
speech before the Hamilton Club, Chicago, April 10, 1899